The present invention relates to a method and apparatus for applying pre-load to a bearing structure of a drive shaft that is directly driven by an electric motor, and a sealed compressor in which this bearing structure is incorporated.
A bearing structure of an electric-motor-driven shaft, wherein the shaft is supported at both ends, is employed, for example, in a sealed compressor.
A typical sealed compressor is shown in FIG. 5. An electric motor 101 is built into a hermetic container 109. A crankshaft 104 is connected to a rotor 102 of the electric motor 101 for driving a compression mechanism 103. A stator 108 of the electric motor 101 is fixed in the hermetic container 109. The crankshaft 104 is supported on the side of the compression mechanism 103 by a main bearing 105 with a greater bearing load, while it is supported by a sub bearing 106 at the side of the electric motor 101 with a smaller bearing load.
The bearing load of the main bearing 105 is set greater than that of the sub bearing 106 since the crankshaft 104 at one end is subject to the centrifugal load generated by eccentric rotation of the crankshaft 104 and an orbiting scroll 107 of the compression mechanism 103, and also subject to the gas pressure exerted thereto when a fluid such as refrigerant is compressed.
Both the main bearing 105 and the sub bearing 106 are roller bearings. It is the common practice to apply a pre-load to the bearing structure in order to suppress the generation of vibration or noise inherently caused by the play that is present between the rolling members and the races of the bearing.
After various experiments and intensive research for developing a compressor that meets the demands of high-speed operation, noise suppression, and durability, the inventors of the present application have found that the conventional method of applying pre-load is not capable of resolving the problems of vibration and noise.
Specifically, the pre-load is uniformly applied to both the main bearing and sub bearing in the conventional method, where a pre-load should be suitably applied to each of the main bearing and the sub bearing in accordance with their bearing loads that are different from each other.
In view of the foregoing, an object of the present invention is to provide a method and apparatus for applying pre-load to the bearing structure of an electric-motor-driven shaft, with which pre-load can act on the bearing in accordance with the difference in bearing load so as to suppress vibration and noise. It is a further object to provide a sealed compressor in which this bearing structure is incorporated.
To accomplish the above object, the present invention provides a method of, and apparatus for, applying pre-load to bearings of a drive shaft that is directly connected to a rotor of an electric motor and is operably connected to a drive load, wherein the bearings support the drive shaft at two locations, i.e., at the side of the electric motor and at the side of the drive load, with respectively different bearing loads. A pre-load is applied to the bearings in an axial direction by providing a resilient member between an inner race of either one or both of the bearings and the drive shaft. In addition, a pre-load is applied in an axial direction to one of the bearings of which bearing load is greater than the other by the weight of the drive shaft and the rotor of the electric motor, either alone or in combination with a magnetic attractive force generated in the electric motor. The rotor of the electric motor is arranged offset with respect to a stator of the electric motor, so that the magnetic attractive force is generated in a direction opposite from a direction of offset of the rotor with respect to the stator while the electric motor is driven.
The above method and apparatus for applying pre-load to bearings of a drive shaft can be advantageously applied to a sealed compressor, comprising a compression mechanism and an electric motor housed in a hermetic container, wherein a crankshaft directly connected to the electric motor is supported at both ends by a main bearing and a sub bearing.
According to the present invention, the resiliency of the resilient member interposed between the inner race of one or both of the bearings acts equally on both of the bearings through the common crankshaft, while the weight of the crankshaft and the rotor of the electric motor and/or the magnetic attractive force generated in the electric motor act on the bearing which is subject to a greater bearing load than the other as a pre-load in the axial direction. As a result, the pre-loads combine with or counterbalance each other in accordance with the position and direction in which the pre-loads are applied to both bearings. Therefore, a pre-load of suitable amount can be respectively applied to each of the bearings in accordance with their different bearing loads. Accordingly, the generation of vibration and noise caused by the play in the bearings during the rotation of the crankshaft can be satisfactorily suppressed.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.